Immunogenetics

• Enza Ferrero (Assistant professor)
• Erica Ortolan (Research technician) 
• Yuliya Yakymiv (Post-doc)
• Sara Marchisio (PhD student)
• Rebecca Maria Casu (master degree student)
• Letizia Vassoney (student)
• Elisa Girotto (student)

We study the interaction between tumor cells and microenvironment and in particular, the molecular mechanisms driving tumor immunosuppression. Among the pathological alterations that give tumor cells invasive potential, disruption of the inflammatory response and the purinergic signaling are emerging as important components of cancer progression. Nucleotide/nucleoside receptor-mediated cell communication is orchestrated by ectonucleotidases, which efficiently hydrolyze ATP, ADP, and AMP to adenosine (ADO). ATP can act as danger signaling whereas adenosine, acts as a negative feedback mechanism to limit inflammation. Extracellular adenosine (eADO) signaling has emerged as an important regulator of immune responses, including anti-tumor immunity. eADO mediates T-cell immunosuppression through the activation of specific receptors, among which the adenosine receptor 2A (A2AR) is the most important. eADO is generated through two pathways. In the canonical pathway, extracellular ATP is hydrolyzed to ADP and AMP by CD39, then AMP is converted into eADO by CD73. The non-classical eADO production is mediated by CD38/CD157 which converts NAD+ into ADPR; then converted by CD203a to AMP, which is hydrolyzed by CD73 to eADO (Figure 1). 

The ectonucleotidases involved in the two adenosinergic pathways are expressed by selected cell populations both in the tumor microenvironment (TME) and in the malignant cells. The role of (ecto)enzymes involved in the coordinated control of ADO metabolism and signaling, and how these distinct, but interrelated molecules interact during tumor progression is poorly understood. We recently reported aberrant expression of CD39 and/or CD73 in the circulating CD4+ T cells from patients with Sézary syndrome (SS) an aggressive, leukemic form of cutaneous T cell lymphoma. We demonstrated that the altered expression of CD39 or CD73 in lymphocytes circulating in the blood and infiltrating the skin in SS patients is an intrinsic feature of each patient since diagnosis, persisting during the progression of the disease, regardless of the therapy administered, with the exception of patients being treated with Mogamulizumab (anti-C-C chemokine receptor 4 monoclonal antibody). CD39 or CD73 have important functional implications. Indeed, in vivo, we found significantly higher levels of AMP in plasma from CD39+ patients compared to both CD73+ patients and healthy subjects. In keeping with this finding, ex vivo experiments demonstrated that both CD39 and CD73 are enzymatically active and that the CD39/CD73/adenosine axis implemented in the TME remarkably contributes to immunosuppression. In vitro, in the CD39+ patients, the CD39/CD73/adenosine axis promotes immunosuppression. These findings support the view that high CD39 expression in SS cells, combined with loss of CD26 (a docking site for adenosine deaminase that inactivates adenosine preventing its binding to A2AR on immune cells) and with abundant expression of CD73 in the TME (Figure 2) drive immunosuppression. Overall our data suggest that directly inhibiting the adenosinergic pathways has the potential to unleash an immune-mediated anti-tumor response via two mechanisms: i) increasing the availability of immunostimulatory eATP released by damaged and/or dying cells, and ii) reducing the generation and accumulation of suppressive ADO within the TME. 

Through better understanding of various immune modulating pathways, superior combination therapies may be developed, and prolonged remissions realized, eventually improving the quality of life for patients. SS cells are usually resistant to chemotherapy and, although clinical responses to a wide variety of biologic agents are seen in 30% to 40% of patients, complete and durable responses are rare. This therapeutic challenge is strengthened by recent studies showing marked genomic heterogeneity in SS affecting a variety of signaling pathways, which suggests that the identification of appropriate small-molecule inhibitors or biological drugs for targeted therapy will also be challenging. Nonetheless, analysis of patient samples over time is an urgent need to identify subgroups of SS patients who may benefit from specific targeted therapies.